TV has become an indispensable electronic product to people in their everydayness. Currently, digital TV has attracted even more interests due to its high resolution and delicacy, anti-interference capacity, which protects the frame quality from weather interference, and a variety of interactive functions and software upgrading functions.
TVs capable of receiving and processing external digital TV signals or TVs with an internal digital TV decoder are normally referred as digital TVs. Despite that TVs capable of receiving and processing the external digital TV signals have become more and more popular, many households still use analog TVs that can only receive analog TV signals. If users decide to continue to use the analog TV which can only receive analog TV signals, a digital TV set-top box needs to be disposed on the analog TV for converting digital TV signals into analog TV signals. By doing so, the analog TV is able to receive the digital TV signals. Through digital processing on the digital TV signals, a horizontal sync signal and a vertical sync signal may be separated from the digital TV signals.
However, if the signal-to-noise ratio (SNR) of the digital TV signal is too low, then the vertical sync signal may have a distortion problem. Thus, errors may occur in the processing of video signals. For example, the video frame may jump up and down.